More factoring of common code

1 files changed, 116 insertions, 0 deletions

diff --git a/comboot.inc b/comboot.inc
new file mode 100644
index 00000000..db199145
--- /dev/null
+++ b/comboot.inc
@@ -0,0 +1,116 @@
+;; $Id$
+;; -----------------------------------------------------------------------
+;;   
+;;   Copyright 1994-2002 H. Peter Anvin - All Rights Reserved
+;;
+;;   This program is free software; you can redistribute it and/or modify
+;;   it under the terms of the GNU General Public License as published by
+;;   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
+;;   Bostom MA 02111-1307, USA; either version 2 of the License, or
+;;   (at your option) any later version; incorporated herein by reference.
+;;
+;; -----------------------------------------------------------------------
+
+;;
+;; comboot.inc
+;; 
+;; Common code for running a COMBOOT image
+;;
+
+;
+; Load a COMBOOT image.  A COMBOOT image is basically a DOS .COM file,
+; except that it may, of course, not contain any DOS system calls.  We
+; do, however, allow the execution of INT 20h to return to SYSLINUX.
+;
+is_comboot_image:
+		and dx,dx
+		jnz near comboot_too_large
+		cmp ax,0ff00h		; Max size in bytes
+		jae comboot_too_large
+
+		;
+		; Set up the DOS vectors in the IVT (INT 20h-3fh)
+		;
+		mov dword [4*0x20],comboot_return	; INT 20h vector
+		mov eax,comboot_bogus
+		mov di,4*0x21
+		mov cx,31		; All remaining DOS vectors
+		rep stosd
+	
+		mov cx,comboot_seg
+		mov es,cx
+
+		mov bx,100h		; Load at <seg>:0100h
+
+		mov cx,[ClustPerMoby]	; Absolute maximum # of clusters
+		call getfssec
+
+		xor di,di
+		mov cx,64		; 256 bytes (size of PSP)
+		xor eax,eax		; Clear PSP
+		rep stosd
+
+		mov word [es:0], 020CDh	; INT 20h instruction
+		; First non-free paragraph
+		mov word [es:02h], comboot_seg+1000h
+
+		; Copy the command line from high memory
+		mov cx,125		; Max cmdline len (minus space and CR)
+		mov si,[CmdOptPtr]
+		mov di,081h		; Offset in PSP for command line
+		mov al,' '		; DOS command lines begin with a space
+		stosb
+
+comboot_cmd_cp:	lodsb
+		and al,al
+		jz comboot_end_cmd
+		stosb
+		loop comboot_cmd_cp
+comboot_end_cmd: mov al,0Dh		; CR after last character
+		stosb
+		mov al,126		; Include space but not CR
+		sub al,cl
+		mov [es:80h], al	; Store command line length
+
+		mov [SavedSSSP],sp
+		mov ax,ss		; Save away SS:SP
+		mov [SavedSSSP+2],ax
+
+		call vgaclearmode	; Reset video
+
+		mov ax,es
+		mov ds,ax
+		mov ss,ax
+		xor sp,sp
+		push word 0		; Return to address 0 -> exit
+
+		jmp comboot_seg:100h	; Run it
+
+; Looks like a COMBOOT image but too large
+comboot_too_large:
+		mov si,err_comlarge
+		call cwritestr
+cb_enter:	jmp enter_command
+
+; Proper return vector
+comboot_return:	cli			; Don't trust anyone
+		lss sp,[cs:SavedSSSP]
+		mov ds,ax
+		mov es,ax
+		sti
+		cld
+		jmp short cb_enter
+
+; Attempted to execute DOS system call
+comboot_bogus:	cli			; Don't trust anyone
+		lss sp,[cs:SavedSSSP]
+		mov ds,ax
+		mov es,ax
+		sti
+		cld
+		mov si,KernelCName
+		call cwritestr
+		mov si,err_notdos
+		call cwritestr
+		jmp short cb_enter
+